The present invention is directed to a ring interferometer which has a coherent light source, at least one light sensitive surface of a detector, a light waveguide which is wound in a coil and has two ends, each end providing a separate coupling point at which light from the coherent source is coupled into the light waveguide and propagated to the opposite end for output coupling therefrom along separate output paths, the interferometer includes an arrangement for receiving the output coupled light traveling in the two separate output paths and combining portions thereof in a superimposed fashion to extend along a superimposed path extending to at least one of the light receiving surfaces.
Ring interferometers of this type serve for example to identify rotations and to measure the angular speed thereof. In so doing, they employ the relativistic Sagnac effect, which produces non-reciprocal transit time differences, which are proportional to the angular speed of the rotation. The Sagnac effect will apply to all polarization states of the light. A measurement is carried out of the transit time difference and thus the angular speed is determined by the integral intensity of the light receiving surfaces of the detectors. However, it should be stressed that this merely represents an example of the use of a ring interferometer and that ring interferometers of the type described in the introduction are also used for other purposes.
In ring inteferometers of this type, a component of the light, which is to be input coupled at the coupling point, is reflected as a result of the jump or change in the index of refraction or other inhomogenities. This reflected component is superimposed upon the light which is output coupled from the light waveguide at this coupling point. The reflected component together with the output coupled light is propagated as interference light towards the light receiving surfaces. The interference light including the reflected component will occur at both coupling points and produces interference in the superimposition zone whereby the intensity of the light being received on the surface of the detector is adulterated. In the present example in which a ring interferometer is used as a rotation sensor, these adulterations will cause simulated or false indications of rotations.